Cycloolefin copolymers having low melt viscosity and low optical attenuation

ABSTRACT

Thermoplastic cycloolefin copolymers (COCs) having low melt viscosity and low optical attenuation, a process for their preparation, and their use as optical waveguides (optical fibers).

The invention relates to thermoplastic cycloolefin copolymers (COCs)having low melt viscosity and low optical attenuation, to a process fortheir preparation, and to their use as optical waveguides (opticalfibers).

Optical waveguides are employed for the transport of light, for examplefor the purpose of illumination or signal transmission. They generallycomprise a cylindrical, light-transmitting core surrounded by a claddinglayer of a likewise transparent material with a lower refractive index.Thin-film optical waveguides comprise, for example, three transparentlayers, where the two outer layers have a lower refractive index thanthe central layer. The conduction of light takes place by totalreflection at the interface. Transparent materials which can be employedare glasses or (organic or inorganic) polymers.

The most widespread polymer for use as an optical wave-guide, polymethylmethacrylate (PMMA), can only be employed at up to about 85° C. due toits low glass transition temperature of about 106° C. Other knowntransparent thermoplastics having higher glass transition temperatures,such as, for example, polycarbonate or aromatic polyesters, containaromatic units in the molecule. These result in increased lightabsorption in the short-wave spectral region. The use of such polymersfor optical waveguides is described in illustrative terms in A. Tanakaet al., SPIE, Vol. 840 (1987).

The heat distortion resistance can be improved by reaction ofpolymethacrylates. An example which may be mentioned is thepolymer-analogous conversion of polymethyl methacrylate intopolymethacrylimide. The copolymerization of poly(meth) acrylate withcomonomers such as methacrylic anhydride or methacrylonitrile also givespolymers of higher heat resistance than unmodified PMMA. Another routeto transparent polymers having increased glass transition temperaturesis the use of (meth)acrylates of (per)halogenated or polycyclicaliphatic alcohols or of substituted phenols. The latter likewise haveincreased light absorption in the shortwave spectral region due to thearomatic units. Although the former compounds give transparent polymershaving high glass transition temperatures, conversion, for example, intooptical fibers is difficult or impossible due to their inherentbrittleness.

All the classes of substances described are hygroscopic due to theirpolar nature. At elevated temperature, the water content in the polymercan cause undesired degradation reactions during conversion, reducingthe practical use value.

However, lower water absorption is exhibited by thermoplastic COCs,which also have increased heat distortion resistance. The completeabsence of chromophores, such as double bonds of all types, means thatthese polymers appear particularly suitable for optical applications. Itshould also be possible to employ these plastics in the area of lightconduction (EP-A 0 355 682 and EP-A 0 485 893).

COCs can be prepared using specific Ziegler catalysts (EP-A 0 355 682),usually using alkylaluminum or alkylaluminum chlorides as cocatalysts.However, these compounds hydrolyze during the work-up process describedto give extremely fine, gelatinous compounds which are difficult tofilter. If alkylaluminum chlorides are employed, chlorine-containingcompounds, such as hydrochloric acid or salts, which are likewisedifficult to separate off, are formed during work-up. If hydrochloricacid is employed for the work-up (EP-A 0 355 682 and EP-A 0 485 893),similar problems arise. In particular in the processing of COCs preparedin this way, a brown coloration occurs. In addition, a known problem inthe preparation of ethylene-containing cycloolefin copolymers is theformation of partially crystalline ethylene polymers as a byproduct.EP-AU 447 072, for example, describes how cycloolefin copolymersprepared by vanadium catalysis (cf. EP-AO 156 464) can be freed frompartially crystalline ethylene polymerization by a complex multistepfiltration. The metallocene catalysts described in EP 404 870, with theexception of isopropylene (9-fluorenyl)cyclopentadienylzirconiumdichloride and diphenylcarbyl(9-fluorenyl)cyclopentadienylzirconiumdichloride, also produce partially crystalline ethylene polymers as abyproduct to the cycloolefin copolymer, as our own detailedinvestigations have shown. However, the higher the content of partiallycrystalline ethyl polymer, the higher the optical attenuation of thematerial.

In addition to excellent transparency, a further important prerequisitefor the use of a polymer for the production of a polymeric optical fiberor an optical waveguide is low melt viscosity in order to improve theprocessing conditions.

The object of the invention was to develop a process for the preparationof COCs which are distinguished by improved melt viscosity, loweroptical attenuation, increased glass transition temperature and lowwater absorption compared with the prior art. A further object was toproduce an optical waveguide whose core material comprises these COCs.

It has now been found that copolymerization of lower alpha-olefins,cyclic olefins and polycyclic olefins using a catalyst system comprisingat least one metallocene catalyst and at least one cocatalyst allows thepreparation of COCs having low melt viscosity if metallocene catalystsof certain symmetries are employed. If the reaction mixture formed afterthe copolymerization is subjected to a specific work-up process, opticalwaveguides having a low optical attenuation of 0.1-5 dB/h, preferably0.2-2 dB/km and particularly preferably 0.3-1.5 dB/km, can be preparedfrom the purified COC and a transparent polymer whose refractive indexis lower than the refractive index of the COC. The polymer may be athermoplatic polymer having a refractive index of from 1.34 to 1.47 (at589 nm).

The invention thus relates to a process for the preparation of COCshaving low melt viscosity by polymerization of from 0.1 to 99.9% byweight, based on the total amount of the monomers, of at least onemonomer of the formula I, II, III or IV ##STR1## in which R¹, R², R³,R⁴, R⁵, R⁶, R⁷ and R⁸ are identical or different and are a hydrogen atomor a C₁ -C₈ -alkyl radical or a C6-C₁₆ -aryl radical, where identicalradicals in the various formulae can have different meanings, from 0 to99.9% by weight, based on the total amount of the monomers, of acycloolefin of the formula V ##STR2## in which n is a number from 2 to10, and from 0.1 to 99.9% by weight, based on the total amount of themonomers, of at least one acyclic 1-olefin of the formula VI ##STR3## inwhich R⁹, R¹⁰, R¹¹ and R¹² are identical or different and are a hydrogenatom or a C₁ -C₈ -alkyl radical or a C₆ -C₁₆ -aryl radical, in solution,in suspension, in the liquid cycloolefin monomer, or cycloolefin monomermixture or in the gas phase, at a temperature of from -78° to 150° C.,at a pressure of from 0.5 to 64 bar, in the presence of a catalystcomprising a metallocene as transition-metal component and analuminoxane of the formula VII ##STR4## for the linear type and/or ofthe formula VIII ##STR5## for the cyclic type, where, in the formulaeVII and VIII, R¹³ is a C₁ -C₆ -alkyl group or phenyl or benzyl, and n isan integer from 2 to 50, where the polymerization is carried out in thepresence of a catalyst whose transition-metal component is at least onecompound of the formula IX ##STR6## in which M¹ is titanium, zirconium,hafnium, vanadium, niobium or tantalum,

R¹⁴ and R¹⁵ are identical or different and are a hydrogen atom, ahalogen atom, a C₁ -C₁₀ -alkyl group, a C₁ -C₁₀ -alkoxy group, a C₆ -C₁₀-aryl group, a C₆ -C₁₀ -aryloxy group, a C₂ -C₁₀ -alkenyl group, a C₇-C₄₀ -arylalkyl group, a C₇ -C₄₀ -alkylaryl group or a C₈ -C₄₀-arylalkenyl group,

m may be one or two, depending on the valency of the central atom M¹,

R¹⁸ is ##STR7## ═BR¹⁹, ═AIR¹⁹, --Ge--, --Sn--, --O--, --S--, ═SO, ═SO₂,═NR¹⁹, ═CO, ═PR¹⁹ or ═P(O) R¹⁹, where R¹⁹, R²⁰ and R²¹ are identical ordifferent and are a hydrogen atom, a halogen atom, a C₁ -C₁₀ -alkylgroup, a C₁ -C₁₀ -fluoroalkyl group, a C₆ -C₁₀ -fluoroaryl group, a C₆-C₁₀ -aryl group, a C₁ -C₁₀ -alkoxy group, a C₂ -C₁₀ -alkenyl group, aC₇ -C₄₀ -arylalkyl group, a C₈ -C₄₀ -arylalkenyl group or a C₇ -C₄₀-alkylaryl group, or R¹⁹ and R²⁰ or R¹⁹ and R²¹, in each case with theatoms connecting them, form a ring,

M² is silicon, germanium or tin,

R¹⁶ and R¹⁷ are different and are a monocyclic or polycyclic hydrocarbonradical which can form a sandwich structure with the central atom M¹,wherein the metallocene of the formula IX has C_(S) -symmetry withrespect to the ligands R¹⁶ and R¹⁷ and with respect to the central atomM¹ connecting them.

In the polymerization, at least one polycyclic olefin of the formula I,II, III or IV, preferably a cycloolefin of the formula I or III ##STR8##in which R¹, R², R³, R⁴, R⁵, R⁶, R⁷ and R⁸ are identical or differentand are a hydrogen atom or a C₁ -C₈ -alkyl radical or a C₁ -C₁₆ -arylradical, where identical radicals in the various formulae can havedifferent meanings, is polymerized.

It is also possible to use a monocyclic olefin of the formula V ##STR9##

in which n is a number from 2 to 10.

Another comonomer is an acyclic 1-olefin of the formula VI ##STR10## inwhich R⁹, R¹⁰, R¹¹ and R¹² are identical or different and are a hydrogenatom or a C₁ -C₈ -alkyl radical, which may also contain a double bond,or a C₆ -C₁₆ -aryl radical. Preference is given to ethylene, propylene,butene, hexene, octene or styrene. Particular preference is given toethene. In addition, it is also possible to employ dienes.

In particular, copolymers of polycyclic olefins of the formulae I and IIare prepared.

The polycyclic olefin (I to IV) is employed in an amount of from 0.1 to99.9% by weight, the monocyclic olefin (V) is employed in an amount offrom 0.1 to 99.9% by weight and the acyclic 1-olefin (VI) is employed inan amount of from 0.1 to 99.9% by weight, in each case based on thetotal amount of the monomers.

The monomers are preferably incorporated in the following ratios:

a) the molar polycyclic olefin (I to IV):1-olefin (VI) monomer ratio inthe corresponding polymers is from 1:99 to 99:1, preferably from 20:80to 80:20;

b) in polymers comprising polycyclic olefins (I to IV) and monocyclicolefins (V), the molar polycyclic olefin:monocyclic olefin ratio is from10:90 to 90:10;

c) in polymers comprising polycyclic olefins (I to IV), monocyclicolefins (V) and 1-olefins (VI), the molar polycyclic olefin:monocyclicolefin:1-olefin monomer ratio is from 93:5:2 to 5:93:2 to 5:5:90, i.e.the molar ratio is within a mixture triangle whose corners aredetermined by the molar ratios 93:5:2, 5:93:2 and 5:5:90;

d) in a), b) and c), polycyclic olefins, monocyclic olefins and1-olefins are also taken to mean mixtures of two or more olefins of theparticular type.

The catalyst used in the polymerization comprises an aluminoxane and atleast one metallocene of the formula IX ##STR11##

In the formula IX, M¹ is a metal from the group comprising titanium,zirconium, hafnium, vanadium, niobium and tantalum, preferably zirconiumand hafnium.

R¹⁴ and R¹⁵ are identical or different and are a hydrogen atom, a C₁-C₁₀ -, preferably C₁ -C₃ -alkyl group, a C₁ -C₁₀ -, preferably C₁ -C₃-alkoxy group, a C₆ -C₁₀, preferably C₆ -C₈ -aryl group, a C₆ -C₁₀ -,preferably C₆ -C8-aryloxy group, a C₂ -C₁₀ -, preferably C₂ -C₄ -alkenylgroup, a C₇ -C₄₀, preferably C₇ -C₁₀ -arylalkyl group, a C₇ -C₄₀ -,preferably C₇ -C₁₂ -alkylaryl group, a C₈ -C₄₀ -, preferably C₅ -C₁₂-arylalkenyl group, or a halogen atom, preferably chlorine.

R¹⁶ and R¹⁷ are different and are a monocyclic or polycyclic hydrocarbonradical which can form a sandwich structure with the central atom M¹.

The metallocene of the formula IX has C_(s) -symmetry with respect tothe ligands R¹⁶ and R¹⁷ and with respect to the central atom M¹connecting them.

R¹⁶ is preferably fluorenyl and R¹⁷ is preferably cyclopentadienyl.

R¹⁸ is a single- or multimembered bridge which links the radicals R¹⁶and R¹⁷ and is ##STR12## ═BR¹⁹, =AlR¹⁹, --Ge--, --Sn--, --O--, --S--,═SO, ═SO₂, ═NR¹⁹, ═CO, ═PR¹⁹ or ═P (O) R¹⁹, where R¹⁹, R²⁰ and R²¹ areidentical or different and are a hydrogen atom, a halogen atom,preferably chlorine, a C₁ --C₁₀ --, preferably C₁ -C₃ -alkyl group, inparticular a methyl group, a C₁ -C₁₀ -fluoroalkyl group, preferably aCF₃ group, a C₆ -C₁₀ -fluoroaryl group, preferably a pentafluorophenylgroup, a C₆ -Cl₁₀, preferably C₆ -C₈ -aryl group, a C₁ -C₁₀, preferablyC₁ -C₄ -alkoxy group, in particular a methoxy group, a C₂ -C₁₀,preferably C₂ -C₄ -alkenyl group, a C₇ -C₄₀, preferably C₇ -C₁₀-arylalkyl group, a C₈ -C₄₀, preferably C₈ -C₁₂ -arylalkenyl group, or aC₇ -C₄₀, preferably C₇ -C₁₂ -alkylaryl group, or R¹⁹ and R²⁰ or R¹⁹ andR²¹, in each case together with the atoms connecting them, form a ring.

M² is silicon, germanium or tin, preferably silicon or germanium.

R¹⁸ is preferably ═CR¹⁹ R²⁰, ═SiR¹⁹ R²⁰, GeR¹⁹ R²⁰, --O--, --S--, ═SO,═PR¹⁹ or ═P(O)R¹⁹.

The metallocenes can be prepared in accordance with the followingreaction scheme: ##STR13##

The above reaction scheme naturally also applies to the cases where R¹⁶═R¹⁷ and/or R¹⁹ ═R²⁰ and/or R¹⁴ ═R¹⁵.

Preferred metallocenes are:

diphenylmethylene(9-fluorenyl)(cyclopentadienyl)zirconium dichloride,isopropylene(9-fluorenyl)cyclopentadienylzirconium dichloride,

methylphenylcarbyl(9-fluorenyl)(cyclopentadienyl)-zirconium dichloride,

or mixtures thereof.

Particular preference is given toisopropylene(9-fluorenyl)cylcopentadienylzirconium dichloride ormixtures thereof.

The cocatalyst is an aluminoxane of the formula VII ##STR14## for thelinear type and/or of the formula VIII ##STR15## for the cyclic type. Inthese formulae, R¹³ is a C₁ -C₆ -alkyl group, preferably methyl, ethyl,isobutyl, butyl or neopentyl, or phenyl or benzyl. Particular preferenceis given to methyl. n is an integer from 2 to 50, preferably 5 to 40.However, the precise structure of the aluminoxane is unknown.

The aluminoxane can be prepared in various ways.

In one of the processes, finely powdered copper sulfate pentahydrate isslurried in toluene, and sufficient trialkylaluminum is added in a glassflask under inert gas at about -20° C. so that about 1 mol of CuSO₄ ·5H₂O is available per 4 Al atoms. After slow hydrolysis with elimination ofalkane, the reaction mixture is left at room temperature for from 24 to48 hours, during which cooling may be necessary so that the temperaturedoes not exceed 30° C. The aluminoxane dissolved in toluene issubsequently separated from the copper sulfate by filtration, and thesolution is evaporated in vacuo. It is assumed that this preparationprocess involves condensation of low-molecular-weight aluminoxanes togive higher oligomers with elimination of trialkylaluminum.

Aluminoxanes are furthermore obtained if trialkyl-aluminum, preferablytrimethylaluminum, dissolved in an inert aliphatic or aromatic solvent,preferably heptane or toluene, is reacted with aluminum salts,preferably aluminum sulfate, containing water of crystallization, at atemperature of from -20° to 100° C. In this reaction, the volume ratiobetween solvent and the alkylaluminum used is from 1:1 to 50:1,preferably 5:1, and the reaction time, which can be monitored viaelimination of the alkane, is from 1 to 200 hours, preferably from 10 to40 hours.

The aluminum salts containing water of crystallization are in particularthose which have a high content of water of crystallization. Particularpreference is given to aluminum sulfate hydrate, in particular thecompounds Al₂ (SO₄)₃ ·16H₂ O and Al₂ (SO₄)₃ ·18H₂ O having theparticularly high water of crystallization contents of 16 and 18 mol ofH₂ O/mol of Al₂ (SO₄)₃ respectively.

A further variant of the preparation of aluminoxanes comprisesdissolving trialkylaluminum, preferably trimethylaluminum, in thesuspending medium, preferably in the liquid monomer, in heptane ortoluene, in the polymerization reactor and then reacting the aluminumcompound with water.

In addition to the processes outlined above for the preparation ofaluminoxanes, there are others which can be used. Irrespective of thepreparation method, all aluminoxane solutions have in common a varyingcontent of unreacted trialkylaluminum, in free form or as an adduct.This content has an effect on the catalytic activity which has not yetbeen explained precisely and varies depending on the metallocenecompound employed.

It is possible to preactivate the metallocene by means of an aluminoxaneof the formula II and/or III before use in the polymerization reaction.This significantly increases the polymerization activity.

The preactivation of the transition-metal compound is carried out insolution. It is preferred here to dissolve the metallocene in a solutionof the aluminoxane in an inert hydrocarbon. Suitable inert hydrocarbonsare aliphatic or aromatic hydrocarbons. Preference is given to toluene.

The concentration of the aluminoxane in the solution is in the rangefrom 1% by weight to the saturation limit, preferably from 5 to 30% byweight, in each case based on the entire solution. The metallocene canbe employed in the same concentration, but is preferably employed in anamount of from 10⁻⁴ to 1 mol per mol of aluminoxane. The preactivationtime is from 5 minutes to 60 hours, preferably from 5 to 60 minutes. Thereaction temperature is from -78° C. to 150° C., preferably from 20° to100° C.

Significantly longer preactivation is possible, but normally neitherincreases nor reduces the activity, but may be appropriate for storagepurposes.

The polymerization is carried out in an inert solvent customary for theZiegler low-pressure process, for example in an aliphatic orcycloaliphatic hydrocarbon; examples of these which may be mentioned arebutane, pentans, hexane, heptane, isooctane, cyclohexane andmethylcyclohexane. It is furthermore possible to use a gasoline orhydrogenated diesel oil fraction which has been carefully freed fromoxygen, sulfur compounds and moisture. It is also possible to usetoluene, decalin and xylene.

Finally, the monomer to be polymerized can also be employed as solventor suspending medium. In the case of norbornene, bulk polymerizations ofthis type are carried out at a temperature above 45° C. The molecularweight of the polymer can be regulated in a known manner; hydrogen ispreferably used for this purpose.

The polymerization is carried out in a known manner in solution, insuspension, in the liquid cycloolefin monomer or cycloolefin monomermixture or in the gas phase, continuously or batchwise, in one or moresteps, at a temperature of from -78° to 150° C., preferably from 20° to100° C. The pressure is from 0.5 to 64 bar and is established either bymeans of the gaseous olefins or with the aid of inert gas.

Particularly advantageous are continuous and multistep processes sincethey allow efficient use of the polycyclic olefin, which is fed asresidual monomer together with the reaction mixture.

The metallocene compound is used here in a concentration, based on thetransition metal, of from 10⁻³ to 10⁻⁷ mol, preferably from 10⁻⁵ to 10⁻⁶mol, of transition metal per dm³ of reactor volume. The aluminoxane isused in a concentration of from 10⁻⁴ to 10⁻¹ mol, preferably from 10⁻⁴to 2·10⁻² mol, per dm³ of reactor volume, based on the aluminum content.In principle, however, higher concentrations are also possible in orderto employ the polymerization properties of various metallocenes.

In the preparation of copolymers, the molar ratios between thepolycyclic olefin and the 1-olefin employed can be varied within a broadrange. The choice of polymerization temperature, the concentration ofthe catalyst components and the molar ratio employed allow theincorporation rate of comonomer to be controlled virtually as desired.In the case of norbornene, an incorporation rate of greater than 40 mol%is achieved.

The mean molecular weight of the copolymer formed can be varied in aknown manner by varying the catalyst concentration or the temperature.

The polydispersity M_(w) /M_(n) of the copolymers is extremely narrow,with values between 1.9 and 3.5. This results in a property profile ofthe polymers which makes them particularly suitable for extrusion.

The copolymerization of polycyclic olefins with acyclic olefins, inparticular with propylene, gives polymers having a viscosity index ofgreater than 20 cm³ /g. Copolymers of norbornene with acyclic olefins,in particular ethylene, have a glass transition temperature of above100° C.

In order to prepare COCs having a low optical attenuation of 0.1-5 dB/m,the reaction mixture is subjected to purification. Purification ispreferably carried out by a process wherein, in a first step, thereaction mixture is suspended with a filtration aid and with a substancewhich precipitates the organometallic compounds in the reaction mixture,the heterogeneous components are filtered off in a second step, and, ina third step, the purified COC is precipitated from the COC filtratewith the aid of a precipitant or the solvent of the COC filtrate isevaporated off.

In step three, it is possible to employ evaporation methods such as, forexample, evaporation with the aid of a flash chamber, a thin-filmevaporator, a ®List compounder (List, England), a vented extruder or a®Diskpack (Farrel, USA).

Substances which precipitate the organometallic compound in the reactionmixture are preferably polar compounds, such as water, ethylene glycol,glycerol and acetic acid. The suspending medium is preferably ahydrocarbon. Particularly suitable filtration aids are kieselguhr, forexample ®Celite 545 (LuV, Hamburg), Perlite, for example ®Celite PerliteJ-100 (LuV), modified cellulose, for example ®Diacel (LuV); porouscarbon and absorptive asbestos fibers are also suitable.

The use of filtration aids enables good depth filtration to be achieved.Continuous or batch filtration techniques can be employed. Filtrationcan be carried out as a pressure filtration or a centrifugation. Thefiltration is preferably carried out by means of pressure filters, forexample by filtration through a nonwoven material, or by skimmercentrifugation. It is also possible to use other conventional filtrationtechniques. The filtered COC solution can be fed continuously orbatchwise a number of times through the same filter so that thefiltration action is further intensified. A suitable precipitant isacetone, isopropanol or methanol.

In order to produce optical waveguides, the resultant polymers, whichhave been subjected to the abovedescribed purification step and havebeen dried, are melted using a ram or screw extruder and forced througha die. A cladding layer of a second polymer is applied to the resultantfilament, by coextrusion or by coating from a solution, the refractiveindex of the second polymer being lower than that of the core material.Suitable cladding materials are polymers and copolymers of4-methylpentene, inter alia olefins, copolymers of ethylene andvinylidene fluoride, with or without addition of other comonomers, suchas, for example, hexafluoropropene, tetrafluoroethylene, terpolymers oftetrafluoroethylene, hexafluoropropene and vinylidene fluoride, ifdesired also ethylene, copolymers of methyl methacrylate andmethacrylates of (partially) fluorinated alcohols, for exampletetrafluoro-n-propyl methacrylate.

In order to produce flat-film optical waveguides, the polymers purifiedby the above-described process are melted in an extruder and forcedthrough a flat-film die. The reflection layer on the surface can beapplied by coextrusion or by coating from solution with a second polymerwhose refractive index is lower than that of the core material.

The invention is described by the examples below.

EXAMPLE Example 1

A clean and dry 75 dm³ polymerization reactor fitted with stirrer wasflushed with nitrogen and then with ethylene and charged with 22,000 gof norbornene melt (Nb) and 6 liters of toluene. The reactor was thenheated to a temperature of 70° C. with stirring, and 3.4 bar of ethylenewere injected. 500 cm³ of a toluene solution of methylaluminumoxane(10.1% by weight of methylaluminoxane having a molecular weight of 1300g/mol, according to cryoscopic determination) were then metered into thereactor, and the mixture was stirred at 70° C. for 15 minutes, duringwhich the ethylene pressure was kept topped up at 3.4 bar. In parallel,350 mg of diphenyl-carbyl-cyclopentadienyl)(9-fluorenyl)zirconiumdichloride were dissolved in 500 cm³ of a toluene solution ofmethylaluminoxane (concentration and quality see above) and preactivatedby standing for 15 minutes. The solution of the complex (cat. solution)was then metered into the reactor. For molecular weight regulation, 0.7liter of hydrogen was introduced at the outset. During thepolymerization, 780 ml/h of hydrogen were metered in continuously. Themixture was then polymerized at 70° C. for 1.5 hours with stirring (750revolutions per minute), during which the ethylene pressure was kepttopped up at 3.4 bar.

The reaction solution was discharged into a 150 liter stirred reactorcontaining 500 g of kieselguhr (®Celite 545, nuV, Hamburg) oralternatively cellulose filtration aid (®Diacel, LuV, Hamburg), 200 mlof water, 0.5 g of peroxide decomposer (®Hostanox 3, Hoechst) and 0.5 gof antioxidant (®Hostanox 03, Hoechst) in 50 liters of a hydrogenateddiesel oil fraction (®Exsol, boiling range 100°-120° C., Exxon). Themixture was stirred at 60° C. for 30 minutes.

A filter cake of 500 g of ®Celite (or alternatively 500 g of cellulose),suspended in 10 liters of ®Exsol, was built up on the filter fabric of a120 liter pressure filter. The polymer solution was filtered through thepressure filter in such a manner that the filtrate was first returned tothe filter for 15 minutes. A pressure of up to 2.8 bar of nitrogen wasbuilt up above the solution.

The filtrate was then filtered through 7 filter cartridges (FluidDynamics, Dynalloy XS64, 5 μm, 0.1 m² / cartridge) mounted in a steelhousing. The polymer solution was stirred into 500 liters of acetone bymeans of a disperser (®Ultraturax) and precipitated. During this, theacetone suspension was circulated through a 680 liter stirred pressurefilter with opened base valve. The base valve was closed, and theproduct was washed three times with 200 1 of acetone. 50 g of stabilizer(®Irganox 1010, Ciba) were added to the final wash. After the finalfiltration, the product was predried at 100° C. in a stream of nitrogenand then dried for 24 hours at 0.2 bar in a drying cabinet. 4160 g ofproduct were obtained. A viscosity index (VI) of 62 cm³ /g (DIN 53728)and a glass transition temperature (T_(g)) of 181° C. were measured onthe product. Its melt viscosity was 400 PaS.

Example 2 (comparative example to Example 1, EP 407 870)

A clean and dry 75 dm³ polymerization reactor fitted with stirrer wasflushed with nitrogen and then with ethylene and charged with 22,000 gof norbornene melt (Nb) and 6 liters of toluene. The reactor was thenheated to a temperature of 70° C. with stirring, and 3.4 bar of ethylenewere injected. 500 cm³ of a toluene solution of methylaluminumoxane(10.1% by weight of methylaluminoxane having a molecular weight of 1300g/mol, according to cryoscopic determination) were then metered into thereactor, and the mixture was stirred at 70° C. for 15 minutes, duringwhich the ethylene pressure was kept topped up at 3.4 bar. In parallel,350 mg of diphenylcarbyl(cyclopentadienyl)(9-fluorenyl)zirconiumdichloride were dissolved in 500 cm³ of a toluene solution ofmethylaluminoxane (concentration and quality see above) and preactivatedby standing for 15 minutes. The solution of the complex (cat. solution)was then metered into the reactor. For molecular weight regulation, 0.7liter of hydrogen was introduced at the outset. During thepolymerization, 780 ml/h of hydrogen were metered in continuously. Themixture was then polymerized at 70° C. for 1.5 hours with stirring (750revolutions per minute), during which the ethylene pressure was kepttopped up at 3.4 bar.

The reactor contents were then quickly discharged into a 150 l stirredvessel containing 200 cm³ of isopropanol in 10 l of Exsol. The mixturewas precipitated in 500 l of acetone and stirred for 10 minutes, and thesuspended polymer solid was then filtered off. The filtered-off polymerwas then added to 200 l of a mixture of two parts of 3 normalhydrochloric acid and one part of ethanol, and this suspension wasstirred for 2 hours. The polymer was then re-filtered, washed with wateruntil neutral and dried at 80° C. and 0.2 bar for 15 hours. 4320 g ofproduct were obtained. A viscosity index VI of 60 cm³ (DIN 53728) and aglass transition temperature (T_(g)) of 182° C. were measured on theproduct. No melt endotherm was found in the DSC.

Example 3 (comparative example to Example 1, EP 407 870)

The process was analogous to Example 1. However, the catalyst used was1200 mg of rac-dimethylsilylbis(1-indenyl)zirconium dichloride. After areaction time of 150 minutes, at an ethylene pressure of 3.2 bar andusing the work-up process described in Example 1, 5070 g of polymer wereobtained, on which a VI of 61 cm³ /g (DIN 53728) and a T_(g) of 179° C.were measured.

                  TABLE 1                                                         ______________________________________                                                  COC (Example 1)                                                                          COC (Example 3)                                          ______________________________________                                        Melt viscosity                                                                            400          2000                                                 (Pa*S)                                                                        ______________________________________                                    

(measured as the zero shear viscosity, i.e. as the approximate viscosityat a shear rate of 0.1 s⁻¹, measurement by capillary viscometer,measurement at T=Tg+120° C.)

Example 4

The polymer from Example 1 is melted in a ram extruder at a barreltemperature of from 210° to 260° C. and forced at a flow rate of 610 cm³/h through a die having an internal diameter of 2 mm. A terpolymer oftetrafluoroethylene, vinylidene fluoride and hexafluoropropene having amelt flow index of 32 g/10 min at 265° C. and a load of 11 kg is meltedin a ram extruder and conveyed at a flow rate of 39 cm³ /h to an annularslit arranged concentrically around the core die. The core/claddingfiber produced is cooled in a spinning bath and taken up at a rate of 35m/min. In order to improve the mechanical properties, the fiber issubsequently stretched at 190° C. in a hot-air oven at a ratio of 1:2.5and then wound up. A core/cladding fiber having a core diameter of 970μm and a cladding diameter of 1 mm is obtained.

Tear strength 4.5 cN/tex (DIN [lacuna])

Elongation at break 27% (DIN [lacuna])

Optical attenuation 1.2 dB/m (at 650 run)

Example 5

The polymer from Example 2 is melted in a ram extruder at a barreltemperature of from 210° to 260° C. and forced at a flow rate of 610 cm³/h through a die having an internal diameter of 2 mm. A terpolymer oftetrafluoroethylene, vinylidene fluoride and hexafluoropropene having amelt flow index of 32 g/10 min at 265° C. and a load of 11 kg is meltedin a ram extruder and likewise conveyed at a flow rate of 39 cm³ /h toan annular slit arranged concentrically around the core die. Thecore/cladding fiber produced is cooled in a spinning bath and taken upat a rate of 5.5 m/min. In order to improve the mechanical properties,the fiber is subsequently stretched at 190° C. in a hot-air oven at aratio of 1:2.5 and then wound up. A core/cladding fiber having a corediameter of 970 μm and a cladding diameter of 1 mm is obtained.

Tear strength 5.2 cN/tex (DIN [lacuna])

Elongation at break 28% (DIN [lacuna])

Optical attenuation 12.2 dB/m (at 650 rim)

Example 6

A polymerization solution was prepared analogously to Example 3, but thesolution was worked up analogously to Example 2, i.e. the polymersolution was not filtered.

The DSC showed, in addition to the glass transition temperature (T_(g)=178° C.), a melt endotherm at 127° C. with a melt enthalpie of 1 J/g,attributable to a partially crystalline ethylene-rich polymer. Thisvalue corresponds to the polyethylene content of from 0.5 to 1% byweight in the dried and purified product. A pressed sheet with athickness of 1 mm was cloudy (pressing conditions: 240° C., 10 minutes,50 bar pressure).

We claim:
 1. A process for the preparation of a cycloolefin copolymer(COC) having low melt viscosity by copolymerization of from 0.1 to 99.9%by weight, based on the total amount of the monomers, of at least onemonomer of the formula I, II, III or IV ##STR16## in which R¹, R², R³,R⁴, R⁵, R⁶, R⁷ and R⁸ are identical or different and are a hydrogen atomor a C₁ -C₈ -alkyl radical or aryl radical, where identical radicals inthe various formulae can have different meanings,from 0 to 99.9% byweight, based on the total amount of the monomers, of a cycloolefin ofthe formula V ##STR17## in which n is a number from 2 to 10, and from0.1 to 99.9% by weight, based on the total amount of the monomers, of atleast one acyclic 1-olefin of the formula VI ##STR18## in which R⁹, R¹⁰,R¹¹ and R¹² are identical or different and are a hydrogen atom or a C₁-C₈ -alkyl radical, in solution, in suspension, in the liquidcycloolefin monomer or cycloolefin monomer mixture or in the gas phase,at a temperature of from -78° to 150° C., at a pressure of from 0.5 to64 bar, in the presence of a catalyst comprising a metallocene astransition-metal component and an aluminoxane of the formula VII##STR19## for the linear type and/or of the formula VIII ##STR20## forthe cyclic type, where, in the formulae VII and VIII, R¹³ is a C₁ -C₆-alkyl group or phenyl or benzyl, and n is an integer from 2 to 50,where the polymerization is carried out in the presence of a catalystwhose transition-metal component is at least one compound of the formulaIX ##STR21## in which M¹ is titanium, zirconium, hafnium, vanadium,niobium or tantalum, R¹⁴ and R¹⁵ are identical or different and are ahydrogen atom, a halogen atom, a C₁ -C₁₀ -alkyl group, a C₁ -C₁₀ -alkoxygroup, a C₆ -C₁₀ -aryl group, a C₆ -C₁₀ -aryloxy group, a C₂ -C₁₀-alkenyl group, a C₇ -C₄₀ -arylalkyl group, a C₇ -C₄₀ -alkylaryl groupor a C₅ -C₄₀ -arylalkenyl group, and m may be one or two, depending onthe valency of the central atom M¹, R¹⁸ is ##STR22## ═BR¹⁹, ═AlR¹⁹,--Ge--, --Sn--, --O--, --S--, ═SO, ═SO₂, ═NR¹⁹, ═CO, ═PR¹⁹ or ═P(O)R¹⁹,where R¹⁹, R²⁰ and R²¹ are identical or different and are a hydrogenatom, a halogen atom, a C₁ -C₁₀ -alkyl group, a C₁ -C₁₀ -fluoroalkylgroup, a C₆ -C₁₀ -fluoroaryl group, a C₆ -C₁₀ -aryl group, a C₁ -C₁₀-alkoxy group, a C₂ -C₁₀ -alkenyl group, a C₇ -C₄₀ -arylalkyl group, aC₈ -C₄₀ -arylalkenyl group or a C₇ -C₄₀ -alkylaryl group, or R¹⁹ and R²⁰or R¹⁹ and R²¹, in each case with the atoms connecting them, form aring, M² is silicon, germanium or tin, R¹⁶ and R¹⁷ are different and area monocyclic or polycyclic hydrocarbon radical which can form a sandwichstructure with the central atom M¹,wherein the metallocene of theformula IX has C_(S) -symmetry with respect to the ligands R¹⁶ and R¹⁷and with respect to the central atom M¹ connecting them, the copolymerbeing subjected, when the copolymerization is complete, to apurification process which results in an optical attenuation of thematerial of from 0.1 to 5 dB/m.
 2. The process as claimed in claim 1,wherein the catalyst used is a metallocene of the formula XI in whichR¹⁶ is fluorenyl and R¹⁷ is cyclopentadienyl.
 3. The process as claimedin claim 2, wherein the metallocene used isdiphenylmethylene(9-fluorenyl)-cyclopentadienylzirconium dichloride. 4.The process as claimed in claim 1, wherein the 1-olefin employed isethylene.
 5. The process as claimed in claim 1, wherein the 1-olefinemployed is ethylene and the polycyclic olefin employed is norbornene.6. The process as claimed in claim 2, wherein, in a first step of thepurification process, the reaction mixture is suspended with afiltration aid and with a substance which precipitates theorganometallic compounds in the reaction mixture, the heterogeneouscomponents are filtered off in a second step, and, in a third step, thepurified COC is precipitated from the COC filtrate with the aid of aprecipitant or the solvent of the COC filtrate is evaporated off.
 7. Acycloolefin copolymer (COC) prepared as claimed in claim
 2. 8. Acycloolefin copolymer (COC) prepared as claimed in claim 5, wherein itsglass transition temperature is above 100° C.
 9. An optical waveguidecomprising a light-transmitting core or a light-transmitting layer and acladding layer of a transparent polymer whose refractive index is lowerthan the refractive index of the light-transmitting medium, wherein thelight-transmitting core or the light-transmitting and/or cladding layercomprises a COC as claimed in claim
 8. 10. An optical waveguide asclaimed in claim 9, wherein the cladding layer comprises a thermoplasticpolymer having a refractive index of from 1.34 to 1.47 (at 589 nm). 11.An optical waveguide as claimed in claim 9, wherein the cladding layercomprises polymers or copolymers of 4-methylpentene and other olefins,copolymers of ethylene and vinylidene fluoride, with or without additionof other comonomers, copolymers of tetrafluoroethylene,hexafluoropropene and vinylidene fluoride, or copolymers of methylmethacrylate and methacrylates of fluorinated or partially fluorinatedalcohols.
 12. A cycloolefin copolymer prepared as claimed in claim 1,wherein less than 0.1% by weight of partially crystalline ethylenepolymer, based on the total weight of the polymer, is formed during thepolymerization.
 13. The process as claimed in 2, wherein the metalloceneused is isopropylene (9-fluorenyl)cyclopentadienylzirconium dichloride.14. An optical waveguide as claimed in claim 11, wherein the claddinglayer contains other comonomers.
 15. An optical waveguide as claimed inclaim 14, wherein the other comonomers are hexafluoropropene,tetrafluoroethylene or mixtures thereof.
 16. An optical waveguide asclaimed in claim 11, wherein the copolymers of tetrafluoroethylenehexafluoropropene and vinylidene fluoride further contain ethylene. 17.An optical waveguide as claimed in claim 11, wherein the methacrylate ofpartially fluorinated alcohols is tetrafluoro-n-propyl methacrylate. 18.A process for the preparation of a cycloolefin copolymer (COC) havinglow melt viscosity by copolymerization of from 0.1 to 99.9% by weight,based on the total amount of the monomers, of at least one monomer ofthe formula I, II, III or IV ##STR23## in which R¹, R², R³, R⁴, R⁵, R⁶,R⁷ and R⁸ are identical or different and are a hydrogen atom or a C₁ -C₈-alkyl radical or aryl radical, where identical radicals in the variousformulae can have different meanings,from 0 to 99.9% by weight, based onthe total amount of the monomers, of a cycloolefin of the formula V##STR24## in which n is a number from 2 to 10, and from 0.1 to 99.9% byweight, based on the total amount of the monomers, of at least oneacyclic 1-olefin of the formula VI ##STR25## in which R⁹, R¹⁰, R¹¹ andR¹² are identical or different and are a hydrogen atom or a C₁ -C₈-alkyl radical, in solution, in suspension, in the liquid cycloolefinmonomer or cycloolefin monomer mixture or in the gas phase, at atemperature of from -78° to 150° C., at a pressure of from 0.5 to 64bar, in the presence of a catalyst comprising a metallocene astransition-metal component and an aluminoxane of the formula VII##STR26## for the linear type and/or of the formula VIII ##STR27## forthe cyclic type, where, in the formulae VII and VIII, R¹³ is a C₁ -C₆-alkyl group or phenyl or benzyl, and n is an integer from 2 to 50,where the polymerization is carried out in the presence of a catalystwhose transition-metal component is at least one compound of the formulaIX ##STR28## in which M¹ is titanium, zirconium, hafnium, vanadium,niobium or tantalum, R¹⁴ and R¹⁵ are identical or different and are ahydrogen atom, a halogen atom, a C₁ -C₁₀ -alkyl group, a C₁ -C₁₀ -alkoxygroup, a C₆ -C₁₀ -aryl group, a C₆ -C₁₀ -aryloxy group, a C₂ -C₁₀-alkenyl group, a C₇ -C₄₀ -arylalkyl group, a C₇ -C₄₀ -alkylaryl groupor a C₈ -C₄₀ -arylalkenyl group, and m may be one or two, depending onthe valency of the central atom M¹, R¹⁸ is ##STR29## ═BR¹⁹, ═AlR¹⁹--Ge--, --Sn--, --O--, --S--, ═SO, ═SO₂, ═NR¹⁹, ═CO, ═PR¹⁹ or ═P(O)R¹⁹,where R¹⁹, R²⁰ and R²¹ are identical or different and are a hydrogenatom, a halogen atom, a C₁ -C₁₀ -alkyl group, a C₁ -C₁₀ -fluoroalkylgroup, a C₆ -C₁₀ -fluoroaryl group, a C₆ -C₁₀ -aryl group, a C₁ -C₁₀-alkoxy group, a C₂ -C₁₀ -alkenyl group, a C₇ -C₄₀ -arylalkyl group, aC₈ -C₄₀ -aryl alkenyl group or a C₇ -C₄₀ -alkylaryl group, or R¹⁹ andR²⁰ or R¹⁹ and R²¹, in each case with the atoms connecting them, form aring, M² is silicon, germanium or tin, R¹⁶ and R¹⁷ are different and area monocyclic or polycyclic hydrocarbon radical which can form a sandwichstructure with the central atom M¹,wherein the metallocene of theformula IX has C_(s) --symmetry with respect to the ligands R¹⁶ and R¹⁷and with respect to the central atom M¹ connecting them, the copolymerbeing subjected, when the copolymerization is complete, to apurification process which results in a polydispersity of from 1.9 to3.5.
 19. A process for the preparation of a cycloolefin copolymer (COC)having low melt viscosity by copolymerization of from 0.1 to 99.9% byweight, based on the total amount of the monomers, of at least onemonomer of the formula I, II, III or IV ##STR30## in which R¹, R², R³,R⁴, R⁵, R⁶, R⁷ and R⁸ are identical or different and are a hydrogen atomor a C₁ -C₈ -alkyl radical or aryl radical, where identical radicals inthe various formulae can have different meanings, from 0 to 99.9% byweight, based on the total amount of the monomers, of a cycloolefin ofthe formula V ##STR31## in which n is a number from 2 to 10, and from0.1 to 99.9% by weight, based on the total amount of the monomers, of atleast one acyclic 1-olefin of the formula VI ##STR32## in which R⁹, R¹⁰, R¹¹ and R¹² are identical or different and are a hydrogen atom or a C₁-C₈ -alkyl radical, in solutions in suspension, in the liquidcycloolefin monomer or cycloolefin monomer mixture or in the gas phase,at a temperature of from -78° to 150° C., at a pressure of from 0.5 to64 bar, in the presence of a catalyst comprising a metallocene astransition-metal component and an aluminoxane of the formula VII##STR33## for the linear type and/or of the formula VIII ##STR34## forthe cyclic type, where, in the formulae VII and VIII, R¹³ is a C₁ -C₆-alkyl group or phenyl or benzyl, and n is an integer from 2 to 50,where the polymerization is carried out in the presence of a catalystwhose transition-metal component is at least one compound of the formulaIX ##STR35## in which M¹ is titanium, zirconium, hafnium, vanadium,niobium or tantalum,R¹⁴ and R¹⁵ are identical or different and are ahydrogen atom, a halogen atom, a C₁ -C₁₀ -alkyl group, a C₁ -C₁₀ -alkoxygroup, a C₆ -C₁₀ -aryl group, a C₆ -C₁₀ -aryloxy group, a C₂ -C₁₀-alkenyl group, a C₇ -C₄₀ -arylalkyl group, a C₇ -C₄₀ -alkylaryl groupor a C₅ -C₄₀ -arylalkenyl group, and m may be one or two, depending onthe valency of the central atom M¹, R¹⁸ is ##STR36## ═BR¹⁹, ═AlR¹⁹,--Ge--, --Sn--, --O----S--, ═SO, ═SO₂ , ═NR¹⁹, ═CO, ═PR¹⁹ or ═P (O)R¹⁹,where R¹⁹, R²⁰ and R²¹ are identical or different and are a hydrogenatom, a halogen atom, a C₁ -C₁₀ -alkyl group, a C₁ -C₁₀ -fluoroalkylgroup, a C₆ -C₁₀ -fluoroaryl group, a C₆ -C₁₀ -aryl group, a C₁ -C₁₀-alkoxy group, a C₂ -C₁₀ -alkenyl group, a C₇ -C₄₀ -arylalkyl group, aC₈ -C₄₀ -arylalkenyl group or a C₇ -C₄₀ -alkylaryl group, or R¹⁹ and R²⁰or R¹⁹ and R²¹, in each case with the atoms connecting them, form aring, M² is silicon, germanium or tin, R¹⁶ and R¹⁷ are different and area monocyclic or polycyclic hydrocarbon radical which can form a sandwichstructure with the central atom M¹, wherein the metallocene of theformula IX has C_(s) -symmetry with respect to the ligands R¹⁶ and R¹⁷and with respect to the central atom M¹ connecting them, the copolymerbeing subjected, when the copolymerization is complete, to apurification process which results in a melt viscosity below 2000 Pa·s.